1. Field of the Invention
The present invention relates to a rear-wheel suspension device for a vehicle, and more particularly to a rear-wheel suspension device for a tricycle vehicle having a front vehicle portion rollably movable in a lateral vertical plane with respect to a rear vehicle portion.
2. Description of the Prior Art p U.S. Pat. No. 3,931,989, which issued Jan. 13, 1976, discloses a known tricycle vehicle having a front frame supporting a single wheel and a rear frame supporting a pair of wheels, the front frame being tiltable laterally with respect to the rear frame. The front and rear frames are connected by a rolling joint having a sleeve bearing with a sleeve thereof fixed to the front frame. The rolling joint has a shaft supporting the rear frame and is located in axial alignment with the sleeve for angular movement only about its own axis with respect to the sleeve. When the known tricycle runs on a bumpy road, the axles of the rear wheels, supported by swingable arms and moving up and down, constantly change their positional relationship with respect to the longitudinal axis of the shaft, which fact obviously results in poor balance or stability between the rear wheels. Since the shaft of the rolling joint is angularly movable only about its own axis, the rear wheels, in order to damp their jumping movement over bumps on the road, are required to be supported by swingable arms other than the shaft through the medium of a support additionally attached to the shaft. The thus constructed rear frame is complicated in structure, and the shaft and hence the rolling joint should be of high rigidity and large-size because a large bending moment is imposed on the shaft by the rear frame. Further, with the conventional arrangement of the rear frame, the tricycle cannot effectively provide riding comfort because a shock absorber and a rear-wheel supporting arm cannot be positioned for optimum shock absorbing ability, and no suitable structure for reducing engine vibrations is provided.